One particular user has this problem, where the system doesn't map the INBOX folder to their actual Inbox. I have completely deleted & expuged their entire account and re-created it, and the problem returned. No other users on the server have this problem.
Phone is a Samsung Galaxy 9, app is Nine. OS is Oreo. Kolab is 16.0.1-14.1.el7.kolab_16.x86_64, on CentOS 7.6.1810.